German Patent Application 3,827,049 discloses a membrane which is produced by applying a crystallisation-promoting layer to a support, for example a metal or ceramic support, and allowing zeolite A to grow thereon from a solution which contains silicate, aluminate and sodium.
In addition, European Patent Application 135,069 discloses a composite membrane which consists of a porous support on which a continuous zeolite layer has been applied, which membrane can be obtained by depositing a gel which contains zeolite constituents on a porous support and allowing the gel to crystallise at elevated temperature.
U.S. Pat. No. 5,019,263 discloses a non-composited microporous membrane consisting of crystalline molecular sieve material, in particular silicon dioxide or zeolite. This membrane is produced by depositing crystalline material of the desired composition from a solution onto an auxiliary carrier, removing the crystalline material from the auxiliary carrier and calcining it. Because of the small thickness (0.1-400 .mu.m) the residual membrane is difficult to handle and has little resistance to substantial differences in pressure.
A method for the production of crystalline zeolite is disclosed in U.S. Pat. No.3,119,660. According to this method amorphous kaolin is pressed to give mouldings and the mouldings are treated at elevated temperature with an alkaline solution which also contains the zeolite constituents; this zeolite is intended for absorption and not for gas separation.